JP2009244839A - Image forming apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and method capable of efficiently removing the unnecessary fogging toner by using a squeezing roller. <P>SOLUTION: This image forming apparatus has an image carrier 10Y, a charging means 11Y, an exposing means 12Y, an developing roller 20Y to develop the formed electrostatic latent images by using a liquid developing agent containing carriers and toner particles, a first squeezing roller 13Y to contact with and squeeze the carrier 10Y developed by the developing roller and applied with a bias voltage Vs<SB>1</SB>, and a second squeezing roller 13Y' to contact with and squeeze the image carrier 10Y squeezed by the first squeezing roller 13Y and applied with a bias voltage Vs<SB>2</SB>, wherein a relation of ¾Vs<SB>1</SB>¾>¾Vs<SB>2</SB>¾ is satisfied. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  In the present invention, the latent image formed on the image carrier is developed with a liquid developer composed of toner and carrier, and the developed image is further transferred to a medium such as recording paper, and the transferred image on the transferred medium. The present invention relates to an image forming apparatus and an image forming method for forming an image by fusing and fixing a toner image.

  Various wet image forming apparatuses that develop a latent image using a high-viscosity liquid developer in which a toner composed of a solid component is dispersed in a liquid solvent and visualize the electrostatic latent image have been proposed. The developer used in this wet image forming apparatus suspends solids (toner particles) in a highly viscous organic solvent (carrier liquid) having electrical insulation properties such as silicon oil, mineral oil, and edible oil. The toner particles are extremely fine with a particle diameter of around 1 μm. By using such fine toner particles, the wet image forming apparatus can achieve higher image quality than a dry image forming apparatus using powder toner particles having a particle diameter of about 7 μm.

  An image forming apparatus using the liquid developer as described above can achieve high image quality, but has various problems to be solved. For example, in an image forming apparatus using a liquid developer, there is a problem that it is difficult to control the liquid developer on a roller such as a photoreceptor (image carrier) or a developing roller because of the liquid. In other words, while using the device, the liquid developer on the roller may wrap around the roller end surface or form a liquid ring on the roller. End up.

In order to deal with the liquid ring, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2007-114380) discloses an image carrier squeeze device that recovers excess developer. This image carrier squeeze device is disposed on the downstream side of the nip portion with the developing roller 20Y so as to face the image carrier 10Y and collects excess developer of the toner image developed on the image carrier 10Y. The image carrier squeeze roller 13Y is formed of an elastic roller member that covers the surface of the elastic member 13-1 and rotates in sliding contact with the image carrier 10Y. The cleaning blade 14Y has a function of recovering excess carrier C and originally unwanted fog toner T ″ from the developer D developed on the image carrier 10Y and increasing the ratio of toner particles in the visible image.
JP 2007-114380 A

  However, in the one described in Patent Document 1, a predetermined bias voltage should be applied to the image carrier squeeze roller in order to collect the originally unnecessary fog toner T ″. There was no disclosure of how much is a problem.

In order to solve the above problems, an image forming apparatus according to the present invention includes an image carrier, a charging unit that charges the image carrier, and a latent image formed by exposing the image carrier. An exposure unit to be formed; a developing unit that develops the latent image using a liquid developer including a carrier and toner particles; and an image carrier that is developed by the developing unit, and a bias voltage Vs ₁ A first squeeze roller that is applied, a second squeeze roller that is in contact with the image carrier squeezed by the first squeeze roller and to which a bias voltage Vs ₂ is applied, and the second squeeze roller A transfer member that abuts on the image carrier squeezed by the image and transfers the image. The absolute value of the bias voltage Vs _{1 and} the absolute value of the bias voltage Vs ₂ are | Vs ₁ |. > | Vs ₂ | of And having the engagement.

The image forming apparatus according to the present invention also includes an image carrier, a charging unit that charges the image carrier, an exposure unit that exposes the image carrier to form a latent image, and the image carrier. The latent image is contacted and developed with a liquid developer containing carrier and toner particles, and a developing unit including a developer carrying member to which a developing bias voltage Vd is applied, and the image carrying developed with the developer carrying member A first squeeze roller that is in contact with the body and to which a bias voltage Vs ₁ is applied;
A second squeeze roller to which a bias voltage value Vs ₂ is applied, abutting against the image carrier squeezed by the second squeeze roller, A transfer member to which the image is transferred, and an absolute value of the developing bias voltage Vd, an absolute value of the bias voltage Vs ₁ , and an absolute value of the bias voltage value Vs ₂ are || Vd | − | Vs ₁ || > || Vs ₁ |-| Vs ₂ ||

The image forming apparatus according to the present invention further includes a temperature detection unit that detects a temperature, and a bias voltage adjustment unit that changes the bias voltage value Vs ₁ according to the temperature detected by the temperature detection unit.

In the image forming apparatus according to the present invention, the bias value adjusting unit changes the bias voltage value Vs ₂ according to the temperature detected by the temperature detecting unit.

In the image forming apparatus according to the present invention, the change amount of the bias voltage value Vs ₁ is larger than the change amount of the bias voltage value Vs ₂ .

  The image forming apparatus according to the present invention further includes a rotation speed changing unit that changes the rotation speed of the image carrier.

Further, in the image forming apparatus according to the present invention, the bias value adjusting unit includes the bias voltage value Vs ₁ and the bias voltage value Vs ₂ according to the rotation speed of the image carrier changed by the rotation speed changing unit. To change.

In the image forming apparatus according to the present invention, the change amount of the bias voltage value Vs ₁ is larger than the change amount of the bias voltage value Vs ₂ .

Further, in the image forming apparatus according to the present invention, the bias voltage adjusting unit is configured such that the absolute value | Vs ₁ | of the bias voltage value and the absolute value of the bias voltage value | Vs ₂ | is increased.

The image forming apparatus according to the present invention further includes a third squeeze roller that is in contact with the image carrier squeezed by the second squeeze roller and to which a bias voltage value Vs ₃ is applied. The absolute value of the voltage Vs _1, the absolute value of the bias voltage Vs ₂ , and the absolute value of the bias voltage value Vs _{3 have} a relationship of | Vs ₁ |> | Vs ₂ |> | Vs ₃ |.

In the image forming method according to the present invention, the image carrier is charged by the charging unit, the latent image is formed by exposing the image carrier to the exposure unit, and the latent image is brought into contact with the image carrier. The image bearing member developed with a liquid developer containing carrier and toner particles in a developing unit having a developing roller and developed with the developing roller is squeezed with a first squeeze roller to which a bias voltage value Vs ₁ is applied. The image carrier squeezed by the first squeeze roller is squeezed by a second squeeze roller to which a bias voltage value Vs ₂ satisfying | Vs ₁ |> | Vs ₂ | is applied. To do.

In the image forming method according to the present invention, the temperature is detected by the temperature detection unit, and the bias voltage value Vs ₁ and the bias voltage value Vs ₂ are changed according to the temperature detected by the temperature detection unit.

In the image forming method according to the present invention, the change amount of the bias voltage value Vs ₁ is larger than the change amount of the bias voltage value Vs ₂ .

In the image forming method according to the present invention, the rotation speed of the image carrier is changed by a rotation speed changing unit, and the bias voltage value Vs ₁ is changed by the rotation speed of the image carrier changed by the rotation speed changing unit. And the bias voltage value Vs ₂ is changed.

In the image forming method according to the present invention, the change amount of the bias voltage value Vs ₁ is larger than the change amount of the bias voltage value Vs ₂ .

  As described above, according to the image forming apparatus and the control method for the image forming apparatus of the present invention, unnecessary fog toner can be efficiently removed by each squeeze roller having a bias voltage value appropriately set.

  Further, according to the image forming apparatus and the image forming method of the present invention, the fog toner can be removed in accordance with the potential decay rate of the image carrier.

  In addition, according to the image forming apparatus and the image forming method of the present invention, the conductive characteristics of the photoconductor change depending on the temperature, and the potential decays faster on the high temperature side. The voltage value can be lowered and fog toner can be appropriately removed.

  Further, according to the image forming apparatus and the image forming method of the present invention, the potential of the first squeeze roller is made larger than that of the second squeeze roller because the potential attenuation due to temperature is larger at the first squeeze roller position. By changing the fog toner, the fog toner can be effectively removed.

  In addition, according to the image forming apparatus and the image forming method of the present invention, the fog toner with an optimum bias voltage value can be used when the printing speed (proportional to the rotation speed of the image carrier) is changed depending on the type of the recording medium. Can be effectively removed.

  Further, according to the image forming apparatus and the image forming method of the present invention, when the printing speed (proportional to the rotation speed of the image carrier) is different, the potential attenuation amount is larger in the preceding squeeze roller. The fog toner is effectively removed by changing the potential of the first squeeze roller larger than that of the squeeze roller.

In connection with the present invention, it is confirmed that the following reference embodiments are also effective configurations. That is, an image forming apparatus according to a reference embodiment of the present invention includes an image carrier made of an amorphous silicon photosensitive member, a charging unit that charges the surface of the image carrier, and an electrostatic latent image by exposing the surface of the image carrier. A developing roller that develops an electrostatic latent image formed in contact with the surface of the image carrier with a liquid developer containing a carrier and toner particles, and forms a developed image. A transfer means for transferring the developed image formed on the predetermined medium, and a surface between the downstream side of the developing roller and the transfer means so as to contact the surface of the image carrier, and a predetermined bias voltage is applied to each of them. has a two squeeze rollers to be applied, the rake of the bias voltage applied to the squeezing roller arranged immediately downstream of the developing roller Vs _1, the bias voltage Vs ₁ is applied When the bias voltage applied to the squeezing roller arranged immediately downstream of Zurora and Vs _2, characterized by having a relationship of Vs _1> Vs _2.

An image forming apparatus according to a reference embodiment of the present invention includes an image carrier made of an amorphous silicon photosensitive member, a charging unit that charges the surface of the image carrier, and an electrostatic latent image formed by exposing the surface of the image carrier. A developing roller that develops an electrostatic latent image formed in contact with the surface of the image carrier with a liquid developer containing a carrier and toner particles, and forms a developed image. A transfer means for transferring the developed image formed on the predetermined medium, and a surface between the downstream side of the developing roller and the transfer means so as to contact the surface of the image carrier, and a predetermined bias voltage is applied to each of them. A bias voltage value applied to the developing roller as Vd, and a bias voltage applied to a first squeeze roller provided immediately downstream of the developing roller. When the Vs _1, the bias voltage applied to the second squeezing roller arranged immediately downstream of said first squeeze roller Vs _2, to, | Vd-
It has a relationship of Vs ₁ |> | Vs ₁ −Vs ₂ |.

An image forming apparatus according to a reference embodiment of the present invention includes a temperature detection unit that detects a temperature, and changes Vs ₁ and Vs ₂ according to a temperature detected by the temperature detection unit. To do.

In the image forming apparatus according to the reference embodiment of the present invention, when Vs ₁ and Vs ₂ are changed according to the temperature detected by the temperature detecting unit, the change amount of Vs ₁ is larger than the change amount of Vs _2. It is characterized by setting.

In addition, the image forming apparatus according to the reference embodiment of the present invention is characterized in that Vs ₁ and Vs ₂ are changed according to the rotation speed of the image carrier.

The image forming apparatus according to the reference embodiment of the present invention sets the change amount of Vs ₁ to be larger than the change amount of Vs ₂ when changing Vs ₁ and Vs ₂ according to the rotation speed of the image carrier. It is characterized by that.

An image forming apparatus according to a reference embodiment of the present invention includes an image carrier made of an amorphous silicon photosensitive member, a charging unit that charges the surface of the image carrier, and an electrostatic latent image formed by exposing the surface of the image carrier. A developing roller that develops an electrostatic latent image formed in contact with the surface of the image carrier with a liquid developer containing a carrier and toner particles, and forms a developed image. A transfer means for transferring the developed image formed on the predetermined medium, and a surface between the downstream side of the developing roller and the transfer means so as to contact the surface of the image carrier, and a predetermined bias voltage is applied to each of them. And m (m is a natural number of 3 or more) applied squeeze rollers, and when the bias of a squeeze roller arranged nth (n ≦ m natural number) from the developing roller is Vs _n , Vs _n-1 It has a relationship of> Vs _n .

The image forming apparatus control method according to the reference embodiment of the present invention includes an image carrier made of an amorphous silicon photosensitive member, a charging unit for charging the surface of the image carrier, and exposing and statically exposing the surface of the image carrier. An exposure unit that forms an electrostatic latent image; a developing roller that develops the electrostatic latent image formed in contact with the surface of the image carrier with a liquid developer including a carrier and toner particles; and the image. A transfer means for transferring the developed image formed on the surface of the carrier to a predetermined medium, and a surface between the downstream side of the developing roller and the transfer means so as to contact the surface of the image carrier, and a predetermined and two squeeze rollers which bias voltage is applied, a method of controlling an image forming apparatus having a bias voltage applied to the squeezing roller arranged immediately downstream of the developing roller Vs ₁ When the bias voltage value bias voltage Vs ₁ is applied to the squeezing roller arranged immediately downstream of the squeeze roller applied Vs _2, to, V
Each bias voltage value is controlled so that the relationship of s ₁ > Vs ₂ is established.

  As described above, according to the image forming apparatus and the control method of the image forming apparatus according to the reference embodiment, unnecessary fog toner can be efficiently removed by each squeeze roller in which the bias voltage value is appropriately set.

  Further, according to the image forming apparatus and the control method for the image forming apparatus according to the reference embodiment, the fog toner can be removed in accordance with the potential decay rate of the image carrier.

  Further, according to the image forming apparatus and the control method for the image forming apparatus according to the reference embodiment, the conductive characteristics of the amorphous silicon photoconductor change depending on the temperature, and the potential decays faster on the high temperature side. In consideration of this, the bias voltage value can be lowered at high temperatures, and fog toner can be appropriately removed.

  Further, according to the image forming apparatus and the control method of the image forming apparatus according to the reference embodiment, the second squeeze roller has a larger amount of potential attenuation due to the temperature at the second squeeze roller position. The fog toner can be effectively removed by greatly changing the potential of the roller.

  In addition, according to the image forming apparatus and the control method for the image forming apparatus according to the reference embodiment, an optimum bias corresponding to the case where the printing speed (proportional to the rotation speed of the image carrier) is changed depending on the type of the recording medium. The fog toner can be effectively removed by the voltage value.

  Further, according to the image forming apparatus and the control method of the image forming apparatus according to the reference embodiment, the potential attenuation amount is larger in the preceding squeeze roller when the printing speed (proportional to the rotation speed of the image carrier) is different. Therefore, the fog toner is effectively removed by changing the electric potential of the first squeeze roller larger than that of the second squeeze roller.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing main components constituting the image forming apparatus according to the embodiment of the present invention. The developing devices 30Y, 30M, 30C, and 30K are arranged at the lower portion of the image forming apparatus with respect to the image forming units of the respective colors arranged at the center of the image forming apparatus, and the intermediate transfer body 40 and the secondary transfer unit (secondary transfer unit) The transfer unit 60 is disposed on the upper part of the image forming apparatus.

  The image forming unit includes image carriers 10Y, 10M, 10C, and 10K, corona chargers 11Y, 11M, 11C, and 11K, and exposure units 12Y, 12M, 12C, and 12K (not shown). The exposure units 12Y, 12M, 12C, and 12K have LED arrays, driver ICs, and wiring boards, and the image carriers 10Y, 10M, 10C, and 10K are uniformly charged by the corona chargers 11Y, 11M, 11C, and 11K. Then, the exposure units 12Y, 12M, 12C, and 12K perform control based on the input image signal to form electrostatic latent images on the charged image carriers 10Y, 10M, 10C, and 10K.

The developing devices 30Y, 30M, 30C, and 30K generally include liquid developers of respective colors including the developing rollers 20Y, 20M, 20C, and 20K, yellow (Y), magenta (M), cyan (C), and black (K). Developer containers (reservoirs) 31Y, 31M, 31C, 31K to be stored, and application rollers for applying liquid developers of these colors from the developer containers 31Y, 31M, 31C, 31K to the developing rollers 20Y, 20M, 20C, 20K. Anilox rollers 32Y, 32M, 32C, 32K, etc. are provided, and image carriers 10Y, 10M, 1
The electrostatic latent image formed on 0C and 10K is developed.

  The intermediate transfer member 40 is an endless belt, and is stretched around a driving roller 41 and tension rollers 42, 52, and 53. The image transfer members 10Y, 10M, 10C, and 10K are primary transfer units 50Y, 50M, 50C, and 50K. It is rotationally driven by the driving roller 41 while abutting. The primary transfer units 50Y, 50M, 50C, and 50K are arranged such that the primary transfer rollers 51Y, 51M, 51C, and 51K are opposed to each other with the image transfer bodies 10Y, 10M, 10C, and 10K sandwiched between the intermediate transfer body 40 and the image transfer bodies 10Y, Using the contact position with 10M, 10C, and 10K as the transfer position, the developed toner images of the respective colors on the image carriers 10Y, 10M, 10C, and 10K are sequentially superimposed and transferred onto the intermediate transfer body 40 to obtain a full-color toner. Form an image.

  In the secondary transfer unit 60, a secondary transfer roller 61 is disposed opposite to the belt driving roller 41 with the intermediate transfer body 40 interposed therebetween, and a cleaning device including a secondary transfer roller cleaning blade 62 is disposed. Then, at the transfer position where the secondary transfer roller 61 is disposed, a single color toner image or a full color toner image formed on the intermediate transfer body 40 is conveyed on the sheet material conveyance path L such as paper, film, cloth, etc. Transfer to recording medium.

  Further, a fixing unit (not shown) is disposed downstream of the path sheet material conveyance path L, and a single color toner image or a full color toner image transferred onto a recording medium such as paper is fused to the recording medium such as paper. And fix.

  Further, the tension roller 42 stretches the intermediate transfer body 40 together with the belt drive roller 41, and a cleaning device including the intermediate transfer body cleaning roller 46 at a portion stretched on the tension roller 42 of the intermediate transfer body 40. Are abutting and arranged.

  Next, the image forming unit and the developing device of the image forming apparatus according to the embodiment of the present invention will be described. FIG. 2 is a sectional view showing main components of the image forming unit and the developing device. Since the configurations of the image forming unit and the developing device for each color are the same, the following description is based on the yellow (Y) image forming unit and the developing device.

  The image forming unit includes an image carrier cleaning roller 16Y, an image carrier cleaning blade 18Y, a corona charger 11Y, an exposure unit 12Y, a developing roller 20Y of the developing device 30Y, a second developing roller 20Y, along the rotation direction of the outer periphery of the image carrier 10Y. A first image carrier squeeze roller 13Y and a second image carrier squeeze roller 13Y ′ are arranged.

  The image carrier cleaning roller 16Y is a roller having a urethane rubber surface layer, and rotates counterclockwise while being in contact with the image carrier 10Y, so that the untransferred liquid developer or the untransferred liquid developer on the image carrier 10Y. To clean. A bias voltage that attracts toner particles in the liquid developer is applied to the image carrier cleaning roller 16Y. Therefore, what is collected by the image carrier cleaning roller 16Y is a liquid developer containing a large amount of toner particles. The liquid developer rich in solid content collected by the image carrier cleaning roller 16Y is scraped off by the image carrier cleaning roller cleaning blade 17Y in contact with the image carrier cleaning roller 16Y and falls vertically downward.

  In contrast, the image carrier cleaning blade 18Y that is in contact with the image carrier 10Y on the downstream side of the image carrier cleaning roller 16Y removes the liquid developer rich in carrier components on the image carrier 10Y with the cleaning blade. It is dropped downward through the holding member 73Y.

The term “solid content rich” refers to a state of a liquid developer that contains more solid content than the liquid developer supplied to the developing device 30Y. On the other hand, the carrier component rich means a state of a liquid developer containing a larger amount of carrier component than the liquid developer supplied to the developing device 30Y. The liquid developer (toner) can be defined as a solid content (toner particles) dispersed in a carrier.

  In the cleaning blade holding member 73Y, both the liquid developer rich in solid content dropped from the image carrier cleaning roller cleaning blade 17Y and the liquid developer rich in carrier component scraped by the image carrier cleaning blade 18Y are mixed. The fit improves the transportability. Further, such improvement in transportability can also contribute to downsizing of the apparatus.

  The image carrier recovery storage unit 80Y includes a solid developer rich liquid developer scraped by the image carrier cleaning roller cleaning blade 17Y and a carrier component rich liquid developer scraped by the image carrier cleaning blade 18Y. It has a concave part that receives both.

  A collecting screw 81Y is provided in the concave portion of the image carrier collecting and storing unit 80Y. When the collecting screw 81Y rotates, the liquid developer received by the spiral blade at the concave portion is collected on the rotating shaft of the collecting screw 81Y. Transport in the direction. The liquid developer conveyed by the recovery screw 81Y is sent to a recovery mechanism (not shown).

  Reference numerals 70Y, 71Y, 72Y, 73Y denote cleaning blade holding members for holding the cleaning blades.

  A cleaning blade 21Y, an anilox roller 32Y, and a compaction corona generator 22Y are disposed on the outer periphery of the developing roller 20Y in the developing device 30Y. A regulating blade 33Y for adjusting the amount of liquid developer supplied to the developing roller 20Y is in contact with the anilox roller 32Y. A blade holding member 75Y holds the regulating blade 33Y. An auger 34Y and a recovery screw 321Y are accommodated in the liquid developer container 31Y.

  A primary transfer roller 51Y of the primary transfer portion is disposed along the intermediate transfer body 40 at a position facing the image carrier 10Y.

  The image carrier 10Y is a photosensitive drum made of a cylindrical member that is wider than the developing roller 20Y and has a photosensitive layer formed on the outer peripheral surface thereof. For example, the image carrier 10Y rotates in a clockwise direction as shown in FIG. The photosensitive layer on the surface layer of the image carrier 10Y is composed of an amorphous silicon photoreceptor. The corona charger 11Y is disposed upstream of the nip portion between the image carrier 10Y and the developing roller 20Y in the rotation direction of the image carrier 10Y, and a voltage is applied from a power supply device (not shown) to charge the image carrier 10Y. Let The exposure unit 12Y irradiates a laser beam onto the image carrier 10Y charged by the corona charger 11Y on the downstream side in the rotation direction of the image carrier 10Y from the corona charger 11Y, and a latent image is formed on the image carrier 10Y. Form.

  Note that, from the beginning to the end of the image forming process, the configuration of the rollers and the like arranged in the preceding stage is defined as being upstream of the configuration of the rollers and the like arranged in the subsequent stage.

  The developing device 30Y includes a compaction corona generator 22Y that performs a compaction action, and a developer container 31Y that stores a liquid developer in a state where toner is dispersed in a carrier at a weight ratio of approximately 20%. The developer container 31Y is also provided with a recovery screw 321Y that recovers the liquid developer that has not been supplied to the anilox roller 32Y.

  The developing device 30Y also includes a developing roller 20Y that carries the liquid developer, an anilox roller 32Y that is a coating roller for applying the liquid developer to the developing roller 20Y, and the amount of liquid developer that is applied to the developing roller 20Y. A regulating blade 33Y for regulating, an auger 34Y supplying the anilox roller 32Y while stirring and conveying the liquid developer, a compaction corona generator 22Y for bringing the liquid developer carried on the developing roller 20Y into a compacted state, and a developing roller 20Y A developing roller cleaning blade 21Y that performs the above cleaning. A cleaning blade holding member 76Y holds the developing roller cleaning blade 21Y.

  The liquid developer contained in the developer container 31Y is a low-concentration (about 1 to 2 wt%) and low-viscosity volatile at room temperature using a conventionally used Isopar (trademark: exon) as a carrier. Is a non-volatile liquid developer having a high concentration and high viscosity and having non-volatility at room temperature. That is, in the liquid developer in the present invention, a solid having an average particle diameter of 1 μm in which a colorant such as a pigment is dispersed in a thermoplastic resin is introduced into a liquid solvent such as an organic solvent, silicon oil, mineral oil, or edible oil. It is a liquid developer having a high viscosity (about 30 to 10,000 mPa · s) which is added together with a dispersant and has a toner solid content concentration of about 20%.

  The auger 34Y is provided in the liquid developer container 31Y so as to be separated from the anilox roller 32Y. When the auger 34Y rotates counterclockwise in FIG. 2, the liquid developer is supplied to the anilox roller 32Y. It has become so.

  The space in the developing container 31Y is divided into two by a partition portion 330Y. One of the spaces divided by the partition unit 330Y is used as a supply storage unit 310Y for supplying the liquid developer, and the other is used as a recovery storage unit 320Y for recovering the liquid developer. The supply storage unit 310Y and the collection storage unit 320Y are separated by the partition unit 330Y so as to be parallel to each other in the axial direction.

  An auger 34Y is rotatably provided in the supply storage unit 310Y, and the liquid developer stored in the supply storage unit 310Y is supplied to the anilox roller 32Y when the auger 34Y rotates during operation of the apparatus. The supply storage unit 310Y and the liquid developer supply pipe 370Y are connected, and the supply of the liquid developer to the supply storage unit 310Y is performed by the liquid developer supply pipe 370Y.

  In addition, a collection screw 321Y is rotatably provided in the collection storage unit 320Y, and the collection screw 321Y rotates during operation of the apparatus, so that liquid developer that has not been used for development or an image carrier squeeze roller cleaning blade. The carrier dropped from the cleaning blade such as 14Y and 14Y ′ is collected.

  The collection storage unit 320Y and the liquid developer collection pipe 371Y are connected to each other. When the collection screw 321Y rotates, the liquid developer is supplied to one end of the collection storage unit 320Y to which the liquid developer collection pipe 371Y is connected. It is designed to be transported. The liquid developer recovered by the recovery storage unit 320Y in this way is guided to a liquid developer recycling mechanism (not shown) by the liquid developer recovery pipe 371Y.

The anilox roller 32Y functions as an application roller that supplies and applies a liquid developer to the developing roller 20Y. The anilox roller 32Y is a cylindrical member, and is a roller having a concave and convex surface formed by grooves engraved in a fine and uniform spiral shape on the surface so that the developer can be easily carried on the surface. The anilox roller 32Y supplies the liquid developer from the developer container 31Y to the developing roller 20Y. During operation of the apparatus, as shown in FIG. 2, the auger 34Y rotates clockwise to supply the liquid developer to the aniloc roller 32Y, and the aniloc roller 32Y rotates counterclockwise to the developing roller 20Y. Apply liquid developer.

  The regulation blade 33Y is an elastic blade having a surface coated with an elastic body, and is composed of a rubber portion made of urethane rubber or the like that comes into contact with the surface of the anilox roller 32Y, and a plate of metal or the like that supports the rubber portion. The Then, the film thickness and amount of the liquid developer carried and conveyed by the anilox roller 32Y are regulated and adjusted, and the amount of liquid developer supplied to the developing roller 20Y is adjusted.

  The developing roller cleaning blade 21Y is made of rubber or the like that comes into contact with the surface of the developing roller 20Y. The developing roller 20Y is arranged downstream of the developing nip portion where the developing roller 20Y comes into contact with the image carrier 10Y in the rotation direction of the developing roller 20Y. The liquid developer remaining on the developing roller 20Y is scraped off and removed.

  The compaction corona generator 22Y is an electric field applying means that increases the charging bias on the surface of the developing roller 20Y. The liquid developer conveyed by the developing roller 20Y is compacted by the compaction corona generator 22Y as shown in FIG. Thus, an electric field is applied from the compaction corona generator 22Y side toward the developing roller 20Y.

  As the electric field applying means for compaction, a compaction roller or the like may be used instead of the corona discharge of the corona discharger shown in FIG. Such a compaction roller is a cylindrical member, is in the form of an elastic roller that is configured by covering an elastic body in the same manner as the developing roller 20Y, and has a conductive resin layer or rubber layer on the surface layer of the metal roller base material. For example, it may be rotated clockwise in the opposite direction to the developing roller 20Y.

  On the other hand, the developer carried on the developing roller 20Y and compacted is developed corresponding to the latent image on the image carrier 10Y by applying a desired electric field at the development nip where the developing roller 20Y contacts the image carrier 10Y. Is done. The developer remaining after development is scraped off and removed by the developing roller cleaning blade 21Y and dropped into the collecting unit in the developer container 31Y for reuse. The carrier and toner that are reused in this way are not in a mixed color state.

  The image carrier squeeze device disposed on the upstream side of the primary transfer collects excess developer of the toner image that is disposed on the downstream side of the developing roller 20Y so as to face the image carrier 10Y and is developed on the image carrier 10Y. As shown in FIG. 2, a first image carrier squeeze roller 13Y and a second image carrier squeeze roller comprising an elastic roller member that covers an elastic body and rotates in sliding contact with the image carrier 10Y as shown in FIG. 13Y ′ and the first image carrier squeeze roller 13Y and the second image carrier squeeze roller 13Y ′, which are pressed and slidably contacted to clean the surface, and are developed on the image carrier 10Y. It has a function of recovering excess carrier and originally unwanted fog toner from the developer and increasing the toner particle ratio in the visible image. As the image carrier squeeze device before the primary transfer, a plurality of image carrier squeeze rollers 13Y and 13Y 'are provided in this embodiment, but they may be constituted by one image carrier squeeze roller. Further, one of the plurality of image carrier squeeze rollers 13Y and 13Y 'may be configured to come into contact with and come into contact with each other according to the state of the liquid developer.

  Unnecessary fog toner is collected by applying appropriate bias voltage values to the first image carrier squeeze roller 13Y and the second image carrier squeeze roller 13Y ′. The bias voltage applied to these is recovered. It will be described later.

In the primary transfer unit 50Y, the developer image developed on the image carrier 10Y is transferred to the primary transfer roller 51Y.
Is transferred to the intermediate transfer body 40. Here, the image carrier 10Y and the intermediate transfer member 40 are configured to move at a constant speed, reducing the driving load of rotation and movement, and suppressing the disturbance effect on the visible toner image of the image carrier 10Y. Yes.

  The intermediate transfer member 40 passes through the nip of the primary transfer portion 50 of each color of yellow (Y), magenta (M), cyan (C), and black (K), and the developed image of the image carrier of each color is transferred to the color overlay. Then, it enters the nip portion of the secondary transfer unit 60.

  The intermediate transfer body 40 that has passed through the secondary transfer unit 60 circulates again to receive the transfer image at the primary transfer unit 50, but the intermediate transfer body 40 is cleaned on the upstream side where the primary transfer unit 50 is executed. Cleaning is performed by a roller 46 or the like.

  The intermediate transfer body 40 has a three-layer structure in which a polyurethane elastic intermediate layer is provided on a polyimide base layer, and a PFA surface layer is further provided thereon. Such an intermediate transfer body 40 is used in such a manner that it is stretched by a driving roller 41 and tension rollers 42, 52, 53 on the polyimide base layer side, and a toner image is transferred on the PFA surface layer side. The intermediate transfer body 40 having elasticity thus formed has good followability and responsiveness to the surface of the recording medium. This is effective for feeding and transferring.

  Next, the time change of the surface potential of the image carrier 10Y made of an amorphous silicon photoreceptor will be described. FIG. 3 is a diagram showing dark attenuation characteristics of the image carrier 10Y used in the image forming apparatus according to the embodiment of the present invention. FIG. 3 shows a change with time after the image carrier 10Y is charged to 600 V in a dark place. As shown in the figure, the image carrier 10Y composed of an amorphous silicon photoconductor gradually loses its potential even in a dark place after being charged to a predetermined potential. Such a potential characteristic is referred to as dark decay. Such dark attenuation is large at an early stage of attenuation, and becomes gradual as time passes.

  FIG. 4 is a diagram showing the main configuration of the image forming unit in the image forming apparatus, and FIG. 5 is a diagram showing the transition of the image carrier surface potential in the image forming process. What is shown on the vertical axis in FIG. 5 is a bias voltage value applied to each member.

  From the moment when the image carrier 10Y is charged by the corona charger 11Y when T = 0, the surface potential of the image carrier 10Y is attenuated by the dark decay as described above. In the present embodiment, in consideration of such dark attenuation characteristics, the bias voltage values of the first image carrier squeeze roller 13Y and the second image carrier squeeze roller 13Y 'are set.

T = 0 time surface of the charged image carrier 10Y by the corona charger 11Y in the, an electrostatic latent image exposed by the exposure unit 12Y at T = T _E is formed by the developing roller 20 at T = T _D The developed image is formed, and the first image carrier squeeze roller 13Y performs the first squeeze at T = T _S1 to collect fog toner together with the surplus carrier, and the second image carrier squeeze at T = T _S2 . A second squeeze is performed by the roller 13Y ′, and the fog toner is collected together with the surplus carrier.

The image carrier surface potential on the left side in FIG. 5 indicates the surface potential of the image carrier at the time T = T _D when it passes through the developing roller 20Y. V _W0 is the potential of the non-exposed portion on the image carrier 10Y, and V _B0 is the potential of the exposed portion. Vd indicates a bias voltage value applied to the developing roller 20Y. The toner particles are positively charged, and at the time T = T _D when the toner particles pass through the developing roller 20Y, the toner particles move while being attracted to the potential V _B0 . The electrostatic latent image formed on the image carrier 10Y is developed by the moved toner particles, and a developed image is formed.

Here, what is referred to as fog toner refers to toner that has moved to the potential V _W0 , which is a non-exposed portion where the toner particles should not move during the development described above. In the present embodiment, the fog toner is efficiently collected by setting appropriate bias voltage values to the first image carrier squeeze roller 13Y and the second image carrier squeeze roller 13Y ′.

The image carrier surface potential at the center in FIG. 5 indicates the surface potential of the image carrier at the time T = T _S1 when it passes through the first image carrier squeeze roller 13Y. The image carrier surface potential in the center of FIG. 5 is generally lower than the left image carrier surface potential (when passing through the developing roller 20Y), but this is due to the dark decay described above. In the center of FIG. 5, V _W1 is the potential of the non-exposed portion on the image carrier 10Y, and V _B1 is the potential of the exposed portion.

In the present embodiment, the bias voltage value Vs ₁ applied to the first image carrier squeeze roller 13Y is set to satisfy Vd> Vs ₁ . This is because the fog toner present in the non-exposed portion V _W1 is moved to the first image carrier squeeze roller 13Y side as indicated by a dotted arrow. In this embodiment, unnecessary fog toner is efficiently removed by setting the bias voltage value applied to the first image carrier squeeze roller 13Y so that Vd> Vs ₁ in consideration of the dark attenuation characteristics. Like to do.

The image carrier surface potential on the right side in FIG. 5 indicates the surface potential of the image carrier at the time T = T _S2 when it passes through the second image carrier squeeze roller 13Y ′. The image carrier surface potential on the right side of FIG. 5 is generally lower than the center image carrier surface potential (when passing through the first image carrier squeeze roller 13Y). It depends on the characteristics. In the right side of FIG. 5, V _W2 is the potential of the non-exposed portion on the image carrier 10Y, and V _B2 is the potential of the exposed portion.

In the present embodiment, the bias voltage value Vs ₂ applied to the first image carrier squeeze roller 13Y ′ is set to satisfy Vd> Vs ₁ > Vs ₂ . This is because the fog toner present in the non-exposed portion V _W2 is moved to the second image carrier squeeze roller 13Y ′ side as indicated by the dotted arrow. As described above, in the present embodiment, in consideration of the dark attenuation characteristics, the bias voltage value applied to the first image carrier squeeze roller 13Y is set so as to satisfy Vd> Vs ₁ > Vs _2. The fog toner is removed efficiently.

As described above, the dark decay characteristic has a large attenuation rate at an early stage, and the attenuation rate tends to be gradual as time passes.
When Vd−Vs ₁ > Vs ₁ −Vs ₂ , the fog toner can be collected more efficiently. Here, considering that the positive / negative setting of the bias voltage depends on the characteristics of the toner used, the bias voltage value is generally set so that | Vd−Vs ₁ |> | Vs ₁ −Vs ₂ | It is good to define.

In the present embodiment, the case of using two squeeze rollers, the first image carrier squeeze roller 13Y and the second image carrier squeeze roller 13Y ′, is generalized, and n squeeze rollers are provided. Think about it. That is, it is assumed that n image carrier squeeze rollers are arranged on the downstream side of the developing roller 20Y until the primary transfer. In such a case, the bias voltage value applied to the image carrier squeeze roller provided immediately downstream of the developing roller 20Y is Vs ₁ , and the image provided immediately downstream of the image carrier squeeze roller to which the bias voltage Vs ₁ is applied. The bias voltage value applied to the carrier squeeze roller is Vs ₂ ,... Applied to the image carrier squeeze roller provided immediately downstream of the image carrier squeeze roller to which the bias voltage Vs _n-2 is applied. that a bias voltage value Vs _n - _1, the bias voltage the bias voltage Vs _n-1 is applied to the image carrier squeezing roller arranged immediately downstream of the image carrier squeezing roller applied Vs _n, and so on when specified, in the present _{invention, Vs 1> Vs 2> ······} > Vs n - 1> may be to have a relationship of Vs _n, that the That. According to this, the fog toner can be efficiently removed by all image carrier squeeze rollers in consideration of the attenuation of the surface potential of the image carrier due to the dark attenuation characteristic.

By the way, some image forming apparatuses change the image forming process speed (that is, the rotational speed of the image carrier) according to the type of recording medium to be image formed such as thick plain paper or thin high-quality paper. It has been. When the concept of the present invention is applied to a device that changes the speed of the image forming process (the rotational speed of the image carrier), the charging from the corona charger 11Y is changed according to the rotational speed of the image carrier 10Y. Since the time required to reach the one image carrier squeeze roller 13Y and the second image carrier squeeze roller 13Y ′ is different, the bias voltage values Vs ₁ and Vs ₂ may be changed according to the rotational speed of the image carrier 10Y. I understand that. In this way, the fog toner can be effectively removed with an optimum bias voltage value in accordance with the case where the printing speed (proportional to the rotation speed of the image carrier) is changed depending on the type of the recording medium.

Further, in the case of changing the bias voltage Vs ₁ and Vs ₂ according to the rotational speed of the image carrier 10Y as described above, larger than the change amount of the bias voltage Vs ₂ the change amount of the bias voltage Vs ₁ It is good to set. This is because the dark attenuation characteristic has a large attenuation rate in the initial stage and decreases with time. That is, when the printing speed (proportional to the rotational speed of the image carrier) is different, the potential attenuation amount is larger in the preceding squeeze roller, and therefore the first image carrier squeeze roller 13Y ′ than the second image carrier squeeze roller 13Y ′. The potential of the roller 13Y is greatly changed. According to such setting of the bias voltage value, the fog toner is more effectively removed.

  Next, changes in dark decay characteristics with temperature and setting of the bias voltage value of the image carrier squeeze roller considering this will be described. FIG. 6 is a diagram showing changes in dark attenuation characteristics due to temperature changes of the image carrier 10Y. FIG. 6 shows the change over time after the image carrier 10Y is charged to 600 V in a dark place with different temperatures. As shown in the figure, the attenuation rate due to dark attenuation of the image carrier 10Y formed of an amorphous silicon photosensitive member becomes more conspicuous as the temperature increases.

  The change in the dark attenuation characteristic due to the temperature change shown in FIG. 6 is added to the setting of the bias voltage value of the image carrier squeeze roller. Here, for the sake of simplicity, the image carrier squeeze roller is considered as a system shown in FIG. 7 having only one first image carrier squeeze roller 13Y.

  FIG. 7 is a diagram illustrating a main configuration of an image forming apparatus including only one image carrier squeeze roller. FIG. 8 is based on the image forming apparatus shown in FIG. 7, and is a diagram showing the transition of the surface potential of the image carrier due to the temperature change in the image forming process. What is shown on the vertical axis in FIG. 8 is a bias voltage value applied to each member.

The surface potential of the image carrier left in FIG. 8, the time T = T _E passing through the exposure units 12Y
2 shows the surface potential of the image carrier. The solid line indicates the surface potential of the image carrier when the temperature is low, V _WEL is the potential of the non-exposed portion on the image carrier 10Y, and V _BEL is the potential of the exposed portion. Also, the dotted line indicates the image carrier surface potential when the temperature is higher than that, V _WEH is the potential of the non-exposed portion on the image carrier 10Y, and V _BEH is the potential of the exposed portion.

  Vd indicates a bias voltage value applied to the developing roller 20Y.

The surface potential of the image carrier at the center in FIG. 8 indicates that when the temperature is low. FIG. 8 shows the surface potential of the image carrier at time T = T _S1 when it passes through the first image carrier squeeze roller 13Y. The image carrier surface potential in the center of FIG. 8 is generally lower than the left image carrier surface potential (low temperature), which is due to the dark decay described above. In the center shown in FIG. 8, V _W1L is the potential of the non-exposed portion on the image carrier 10Y, and V _B1L is the potential of the exposed portion.

The image carrier surface potential on the right side in FIG. 8 shows that when the temperature is higher than that shown in the center. FIG. 8 shows the surface potential of the image carrier at time T = T _S1 when it passes through the first image carrier squeeze roller 13Y. The image carrier surface potential on the right side in FIG. 8 is generally lower than the image carrier surface potential (temperature high) on the left side, but this is due to the dark decay characteristics described above. In the right side of FIG. 8, V _W2 is the potential of the non-exposed portion on the image carrier 10Y, and V _B2 is the potential of the exposed portion.

  Further, the image carrier surface potential (high temperature) on the right side of FIG. 8 is generally lower than the image carrier surface potential (low temperature) on the center side in FIG. 8 due to the temperature characteristics of dark decay.

  In the present embodiment, in consideration of the dark decay temperature characteristics as described above, temperature detection means for detecting a temperature (not shown) is provided, and the image carrier squeeze is determined according to the temperature detected by the temperature detection means. The bias voltage value applied to the roller is changed. This is the same in the case of the image forming apparatus including the first image carrier squeeze roller 13Y and the second image carrier squeeze roller 13Y '. Depending on the temperature, the conductive characteristics of the amorphous silicon photoreceptor change, and the potential decays faster on the high temperature side. However, taking such changes into account, the bias voltage value is lowered at high temperatures to remove fog toner appropriately.

Further, bias voltage values Vs ₁ and Vs according to the temperature detected by the temperature detecting means.
When changing s ₂ , the change amount of the bias voltage value Vs ₁ is set larger than the change amount of the bias voltage value Vs ₂ . That is, since the potential attenuation amount due to temperature is larger at the position of the second image carrier squeeze roller 13Y ′, the potential of the second image carrier squeeze roller 13Y ′ is changed more greatly than the first image carrier squeeze roller 13Y. Thus, fog toner can be effectively removed.

Next, examples of the present invention will be described.
Example 1
The image carrier 10 made of an amorphous silicon photosensitive member is first charged to a predetermined surface potential by a corona charger 11. At this time, the charging potential of the image carrier 10 is about 500 to 600V. Thereafter, the image unit (black portion) is irradiated with light by the exposure unit 12 and the electric charge charged by the charger is canceled so that the surface potential becomes about 50 to 100V. Moreover, light is not irradiated to the non-image part (white part). However, the surface potential decays naturally even when not exposed to light. This is called dark decay as described above.

  From this point, even when the charged potential of the image carrier 10 is applied to 600 V, the development position of the developing roller 20 and the time until the image carrier 10 reaches the squeeze position of the first image carrier squeeze roller 13Y and the second image carrier squeeze roller 13Y ′. It can be seen that the potential decreases. Moreover, the way of dropping the potential is fast immediately after charging, and thereafter the attenuation gradually becomes gentle.

  In order to remove the fog without aggregating the toner with the first image carrier squeeze roller 13Y and the second image carrier squeeze roller 13Y ′, it is desirable to make the potential 50V to 100V lower than the surface potential of the image carrier 10. . If it is lower than this, the toner removed by squeeze will aggregate, making it difficult to clean and recycle. On the other hand, if it is too high, the fog cannot be effectively removed, and the white portion of the printed matter becomes dirty.

  Therefore, the following experiment was conducted with the layout of the corona charger 11Y, the exposure unit 12Y, the developing roller 20Y, the first image carrier squeeze roller 13Y, and the second image carrier squeeze roller 13Y 'shown in FIG. The diameter of the image carrier 10Y is 78 mm, and changing the speed of the image carrier 10Y changes the time to reach the development position and squeeze position, so that the squeeze bias condition also changes. The dark decay also changes with temperature and humidity, so the effect was confirmed by changing the squeeze bias condition.

The φ78 image carrier 10Y is driven at a photoreceptor speed of 210 mm / sec, and the charged potential of the image carrier 10Y is set to 600V. Here, in order to remove the fog on the photosensitive member, the toner is positively charged. Therefore, the squeeze bias voltage values of the first image carrier squeeze roller 13Y and the second image carrier squeeze roller 13Y ′ are determined from the surface potential of the image carrier. Need to be low. Therefore, in accordance with the dark decay of the image carrier 10Y, the bias of Vs ₂ is made lower than the bias voltage value Vs _{1 and} (Vs ₁ −Vs ₂ ) is made smaller than (Vd−Vs ₁ ). With this setting, the fog could be removed without agglomerating the toner.

（実施例２）
同様にφ７８の感光体で、像担持体１０Ｙを速度２７０ｍｍ／ｓｅｃで駆動し、像担持体１０Ｙの帯電電位を６００Ｖとする。像担持体１０Ｙの暗減衰にあわせて、バイアス電圧値Ｖｓ₁よりバイアス電圧値Ｖｓ₂のバイアスを低くし、（Ｖｄ―Ｖｓ₁）より（Ｖｓ₁―Ｖｓ₂）を小さくなるように、表１のように設定した。このようにすることで、トナーを
凝集させずにカブリを除去することができた。
（実施例３）
同様にφ７８の感光体で、像担持体１０Ｙの速度１５０ｍｍ／ｓｅｃで駆動し、像担持体１０Ｙの帯電電位を６００Ｖとする。像担持体１０Ｙの暗減衰にあわせて、バイアス電圧値Ｖｓ₁よりバイアス電圧値Ｖｓ₂のバイアスを低くし、（Ｖｄ―Ｖｓ₁）より（Ｖｓ₁―Ｖｓ₂）を小さくなるように、表１のように設定した。このようにすることで、トナーを
凝集させずにカブリを除去することができた。
（実施例４）
同様にφ７８の感光体で、像担持体１０Ｙの速度２１０ｍｍ／ｓｅｃで駆動し、像担持体１０Ｙの帯電電位を６００Ｖとする。像担持体１０Ｙの暗減衰にあわせて、バイアス電圧値Ｖｓ₁よりバイアス電圧値Ｖｓ₂のバイアスを低く、バイアス電圧値Ｖｓ₂よりバイア
ス電圧値Ｖｓ３のバイアスを低くし、（Ｖｄ―Ｖｓ₁）より（Ｖｓ₁―Ｖｓ₂）を小さく、
（Ｖｓ₁―Ｖｓ₂）より（Ｖｓ₂―Ｖｓ₃）を小さくなるように、表１のように設定した。このようにすることで、トナーを凝集させずにカブリを除去することができた。図９は実施
例４の画像形成装置の構成を示すものである。

(Example 2)
Similarly, with the photoconductor of φ78, the image carrier 10Y is driven at a speed of 270 mm / sec, and the charged potential of the image carrier 10Y is set to 600V. In accordance with the dark decay of the image carrier 10Y, the bias of the bias voltage Vs ₂ than the bias voltage Vs ₁ is lowered, so as to reduce the (Vs ₁ -Vs ₂₎ than (Vd-Vs _1), Table 1 Was set as follows. By doing so, the fog could be removed without aggregating the toner.
(Example 3)
Similarly, a φ78 photoconductor is driven at a speed of 150 mm / sec of the image carrier 10Y, and the charged potential of the image carrier 10Y is set to 600V. In accordance with the dark decay of the image carrier 10Y, the bias of the bias voltage Vs ₂ than the bias voltage Vs ₁ is lowered, so as to reduce the (Vs ₁ -Vs ₂₎ than (Vd-Vs _1), Table 1 Was set as follows. By doing so, the fog could be removed without aggregating the toner.
Example 4
Similarly, a φ78 photoconductor is driven at a speed of 210 mm / sec of the image carrier 10Y, and the charged potential of the image carrier 10Y is set to 600V. In accordance with the dark decay of the image carrier 10Y, the bias voltage Vs ₁ than the bias voltage Vs ₂ of the low bias, to lower the bias of the bias voltage Vs3 than the bias voltage Vs _2, from (Vd-Vs ₁₎ (Vs ₁ -Vs ₂ )
Table 1 is set so that (Vs ₂ -Vs ₃ ) is smaller than (Vs ₁ -Vs ₂ ). By doing so, the fog could be removed without aggregating the toner. FIG. 9 shows the configuration of the image forming apparatus of the fourth embodiment.

  As described above, according to the image forming apparatus and the control method for the image forming apparatus of the present invention, unnecessary fog toner can be efficiently removed by each squeeze roller having a bias voltage value appropriately set.

  Further, according to the image forming apparatus and the control method of the image forming apparatus of the present invention, the fog toner can be removed in accordance with the potential decay rate of the image carrier.

  Further, according to the image forming apparatus and the control method for the image forming apparatus of the present invention, the conductive characteristics of the amorphous silicon photoconductor change depending on the temperature, and the potential decays faster on the high temperature side. Thus, the bias voltage value can be lowered at high temperatures, and fog toner can be appropriately removed.

  Further, according to the image forming apparatus and the control method for the image forming apparatus of the present invention, the second squeeze roller has a larger amount of potential attenuation due to the temperature at the second squeeze roller position. The fog toner can be effectively removed by greatly changing the potential.

  Further, according to the image forming apparatus and the control method for the image forming apparatus of the present invention, an optimum bias voltage value corresponding to the case where the printing speed (proportional to the rotation speed of the image carrier) is changed depending on the type of the recording medium. Thus, fog toner can be effectively removed.

  Further, according to the image forming apparatus and the control method of the image forming apparatus of the present invention, when the printing speed (proportional to the rotation speed of the image carrier) is different, the amount of potential attenuation is larger in the preceding squeeze roller. The fog toner is effectively removed by changing the potential of the first squeeze roller larger than that of the second squeeze roller.

  Next, another embodiment of the present invention will be described. FIG. 10 is a diagram showing main components constituting an image forming apparatus according to another embodiment of the present invention. In this embodiment, the surface photosensitive layers of the image carriers 10Y, 10M, 10C, and 10K are configured by an organic photoconductor (OPC) in addition to an amorphous silicon photoconductor. In consideration of the case, a bias voltage setting is proposed. In FIG. 10, the same reference numerals as those in the previous embodiment are indicated, and the description thereof will be omitted. However, in the present embodiment, it is assumed that either an amorphous silicon photoconductor or an organic photoconductor is used as the image carrier as described above.

  In the image forming apparatus 1 according to another embodiment, the sheet material set in the sheet feeding cassette 5 is sent to the sheet material conveyance path L by the pickup roller 6 one by one at a predetermined timing. In the sheet material conveyance path L, the sheet material is conveyed to the secondary transfer position by the conveyance roller pair 7, 7 ′, and the single color toner image or the full color toner image formed on the intermediate transfer body 40 is transferred to the sheet material. . The sheet material that has been secondarily transferred is further conveyed to the fixing unit 90 by the conveying roller pair 7 ″. The fixing unit 90 includes a heating roller 91 and a pressure roller 92 urged toward the heating roller 91 with a predetermined pressure. A sheet material is inserted between the nips and transferred onto the sheet. The single color toner image or full color toner image thus formed is fused and fixed to a sheet material such as paper.

The bias voltage Vs ₁ application unit 110 collects unnecessary fog toner on the image carrier by applying the bias voltage Vs ₁ to the first image carrier squeeze roller 13Y at a predetermined timing and voltage. . Also, the bias voltage Vs ₂ applying means 120 is:
By applying a bias voltage Vs ₂ to the second image carrier squeeze roller 13Y ′ at a predetermined timing and voltage, unnecessary fog toner on the image carrier is collected.

In the image forming apparatus 1, the image forming process speed (that is, the rotational speed of the image carrier) is changed according to the type of recording medium to be image formed, such as thick plain paper or thin high-quality paper. The configuration for this is the rotation speed changing means 130. The rotation speed changing unit 130 has a function capable of comprehensively changing the rotation speed of the intermediate transfer member, the conveyance speed in the sheet material conveyance path, the rotation speed in each color developing device, and the like. The control of each means such as the bias voltage Vs ₁ applying means 110, the bias voltage Vs ₂ applying means 120, and the rotation speed changing means 130 is performed by a CPU (not shown).

  The characteristics of the amorphous silicon photoreceptor or the organic photoreceptor that can be used for the image carrier of the image forming apparatus 1 according to another embodiment will be described. FIG. 11 is a diagram showing the dark decay characteristics of the amorphous silicon photoreceptor and the organic photoreceptor. FIG. 11 illustrates the difference in the dark decay rate between the amorphous silicon photoconductor and the organic photoconductor. As shown in the figure, the amorphous silicon photoconductor has a faster decay rate than the organic photoconductor. Note that since the organic photoreceptor is a negatively charged photosensitive material, the dark decay characteristic is attenuated from −500 V to 0 V, but in the figure, the absolute value of the potential is taken to compare with the amorphous silicon photoreceptor. I can do it.

  The amorphous silicon photoreceptor used as the image carrier in the previous embodiment was a positively charged photosensitive material, but the organic photoreceptor that can be used in other embodiments is a negatively charged photosensitive material. The concept of the present invention can also be applied to such a negatively charged photosensitive material.

This will be described with reference to FIG. FIG. 12 is a diagram showing the transition of the surface potential of the image carrier in the image forming process when a negatively charged image carrier is used. 12 can be viewed in the same way as the diagram shown in FIG. 5, and the description of the details is omitted. In FIG. 12, Vs ₁ , Vs ₂ , and Vd all take negative values.

  Even when an organic photoreceptor is used as the image carrier, this fog toner can be efficiently used by setting appropriate bias voltage values to the first image carrier squeeze roller 13Y and the second image carrier squeeze roller 13Y ′. to recover.

The image carrier surface potential at the center in FIG. 12 indicates the surface potential of the image carrier at the time T = T _S1 when passing through the first image carrier squeeze roller 13Y. The overall image carrier surface potential in FIG. 5 is generally higher than the left image carrier surface potential (when passing through the developing roller 20Y), but this is due to the dark decay described above. In the center of FIG. 5, V _W1 is the potential of the non-exposed portion on the image carrier 10Y, and V _B1 is the potential of the exposed portion.

In the embodiment using the negatively charged image carrier, the bias voltage value Vs ₁ applied to the first image carrier squeeze roller 13Y is set so that Vs ₁ > Vd. This is because the fog toner present in the non-exposed portion V _W1 is moved to the first image carrier squeeze roller 13Y side as indicated by a dotted arrow. In the present embodiment, in consideration of dark attenuation characteristics, unnecessary fog toner is efficiently removed by setting a bias voltage value to be applied to the first image carrier squeeze roller 13Y so that Vs ₁ > Vd. Like to do.

The image carrier surface potential on the right side in FIG. 12 indicates the surface potential of the image carrier at time T = T _S2 when it passes through the second image carrier squeeze roller 13Y ′. The image carrier surface potential on the right side of FIG. 12 is generally higher than the central image carrier surface potential (when passing through the first image carrier squeeze roller 13Y). This is due to the attenuation characteristics. In the right side of FIG. 12, V _W2 is the potential of the non-exposed portion on the image carrier 10Y, and V _B2 is the potential of the exposed portion.

When an organic photoreceptor is used as the image carrier, the bias voltage value Vs ₂ applied to the first image carrier squeeze roller 13Y ′ is set so that Vs ₂ > Vs ₁ > Vd. This is because the fog toner present in the non-exposed portion V _W2 is moved to the second image carrier squeeze roller 13Y ′ side as indicated by the dotted arrow. As described above, in this embodiment, in consideration of the dark decay characteristics of the negatively charged photosensitive material, the bias voltage Vs ₁ applying unit 110 and the bias voltage Vs ₂ applying unit 120 satisfy Vs ₂ > Vs ₁ > Vd. By setting bias voltage values to be applied to the first image carrier squeeze roller 13Y and the second image carrier squeeze roller 13Y ′, unnecessary fog toner is efficiently removed. Here, considering the case of including an example of a positively charged amorphous silicon photoconductor as the image carrier, each bias voltage value is set so that | Vd |> | Vs ₁ |> | Vs ₂ | It is good to set. According to this, fog toner can be removed in accordance with the potential decay rate of the image carrier.

As described above, the dark decay characteristic has a large attenuation rate at an early stage, and the attenuation rate tends to be gradual as time passes. Therefore, in consideration of such a tendency, the bias voltage Vs _{1 is} applied. When the bias voltage value is set as | Vd−Vs ₁ |> | Vs ₁ −Vs ₂ | by the means 110 and the bias voltage Vs ₂ applying means 120, the fog toner can be collected more efficiently. Here, considering the case of including an example of a positively charged amorphous silicon photoconductor as the image carrier, the general formula is || Vd |-| Vs ₁
The bias voltage value may be determined so that ||> || Vs ₁ |-| Vs ₂ || According to this, fog toner can be removed in accordance with the potential decay rate of the image carrier.

Consider a generalized case where n squeeze rollers are provided. That is, n image carrier squeeze rollers are arranged on the downstream side of the developing roller 20 until the primary transfer. In such a case, even if an amorphous silicon photoconductor or an organic photoconductor is used as the image carrier 10, it is generalized that | Vs ₁ | >> | Vs ₂ | >> | Vs ₃ | _{·> | Vs n - 1 |} > | Vs n | relationship may be set each bias voltage value so as to have a, a fact. According to this, the fog toner can be efficiently removed by all image carrier squeeze rollers in consideration of the attenuation of the surface potential of the image carrier due to the dark attenuation characteristic.

  Next, changes in dark decay characteristics with temperature and setting of the bias voltage value of the image carrier squeeze roller considering this will be described. As described above, the attenuation rate due to dark attenuation of the image carrier 10 formed of an amorphous silicon photosensitive member becomes more conspicuous as the temperature increases. The same can be said for the organic photoconductor. Therefore, the temperature change in the image forming apparatus 1 is detected by the temperature detecting means 9, and the setting of the bias voltage value of the image carrier squeeze roller is changed according to the detected temperature, thereby collecting the fog toner more efficiently. An embodiment to be described will be described.

First, an embodiment in which only the bias voltage value Vs ₁ is changed by the bias voltage Vs ₁ applying unit 110 according to the temperature detected by the temperature detecting unit 9 can be mentioned.
In such embodiments, bias voltage Vs ₂ application means 120, it is not necessary to change the bias voltage value, it is possible to simplify the configuration of the bias voltage Vs ₂ application means 120. Further, fog toner is removed intensively by the first image carrier squeeze roller 13Y which is the first squeeze means after development.

Further, an embodiment in which only the bias voltage value Vs ₂ is changed by the bias voltage Vs ₂ applying means 120 according to the temperature detected by the temperature detecting means 9 can be mentioned.
In such embodiments, bias voltage Vs ₁ application means 110, it is not necessary to change the bias voltage value, it is possible to simplify the configuration of the bias voltage Vs ₁ application means 110. Further, fog toner is removed intensively by the second image carrier squeeze roller 13Y ′ which is a squeeze means immediately before transfer.

Further, the bias voltage value Vs ₁ and the bias voltage value Vs ₂ are both changed by the bias voltage Vs ₁ applying means 110 and the bias voltage Vs ₂ applying means 120 according to the temperature detected by the temperature detecting means 9. Can be mentioned. According to such an embodiment, it is possible to perform appropriate fog toner removal according to the temperature with the first and second squeeze rollers.

Further, when both the bias voltage value Vs ₁ and the bias voltage value Vs ₂ are changed by the bias voltage Vs ₁ applying means 110 and the bias voltage Vs ₂ applying means 120, the change amount of the bias voltage value Vs ₁ is the above-mentioned amount of change. The bias voltage value Vs ₂ may be changed to be larger than the change amount. According to such an embodiment, the first squeeze roller position has a larger amount of potential attenuation due to temperature. Therefore, by changing the potential of the first squeeze roller larger than that of the second squeeze roller, the fog toner Can be effectively removed.

By the way, in the image forming apparatus 1, the image forming process speed (that is, the rotational speed of the image carrier) is changed according to the type of recording medium to be image formed such as thick plain paper or thin high-quality paper. Such a change in the speed of the image forming process (the rotational speed of the image carrier) is controlled by the rotational speed changing means 130, and the rotational speed of the image carrier 10 and the like changed by the rotational speed changing means 130 is changed. Accordingly, the bias voltage value Vs ₁ and the bias voltage value Vs ₂ are changed by the bias voltage Vs ₁ application unit 110 and the bias voltage Vs ₂ application unit 120, respectively. The reason for adopting such a configuration is that the time required to reach the first image carrier squeeze roller 13 and the second image carrier squeeze roller 13 from charging by the corona charger 11 according to the rotational speed of the image carrier 10. Because it is different. In this way, the fog toner can be effectively removed with an optimum bias voltage value in accordance with the case where the printing speed (proportional to the rotation speed of the image carrier) is changed depending on the type of the recording medium.

At this time, it is desirable that the amount of change of the bias voltage value Vs ₁ by the bias voltage Vs ₁ applying unit 110 is set larger than the amount of change of the bias voltage value Vs ₂ by the bias voltage Vs ₂ applying unit 120. This is because the dark attenuation characteristic has a large attenuation rate in the initial stage and decreases with time. That is, when the printing speed (proportional to the rotational speed of the image carrier) is different, the potential attenuation amount is larger in the preceding squeeze roller, and therefore the first image carrier squeeze roller 13Y ′ than the second image carrier squeeze roller 13Y ′. The potential of the roller 13Y is greatly changed. According to such setting of the bias voltage value, the fog toner is more effectively removed.

The bias voltage value Vs ₁ and the bias voltage value Vs are applied by the bias voltage Vs ₁ application unit 110 and the bias voltage Vs ₂ application unit 120 according to the rotation speed of the image carrier 10 or the like changed by the rotation speed change unit 130. ₂ should be increased. In this way, the fog toner can be effectively removed with an optimum bias voltage value in accordance with the case where the printing speed (proportional to the rotation speed of the image carrier) is changed depending on the type of the recording medium.

At this time, it is preferable that the change amount of the bias voltage value Vs ₁ is set to be larger than the change amount of the bias voltage value Vs ₂ . According to such an embodiment, since the potential attenuation amount is larger at the position of the first squeeze roller, the fog toner is effective by changing the potential of the first squeeze roller larger than that of the second squeeze roller. Can be removed.

Next, examples of the present invention will be described.
(Example 5)
Table 2 shows parameters such as an applied bias voltage value in Example 5. The φ78 image carrier 10 is driven at a photoreceptor speed of 210 mm / sec, and the charged potential of the image carrier 10 is set to 600V. Here, when the temperature is 25 ° C., 440 V is applied to the first image carrier squeeze roller 13 by the bias voltage Vs ₁ application unit 110, and 410 V is applied to the second image carrier squeeze roller by the bias voltage Vs ₂ application unit 120. 13 'is applied. When 35 ° C. is detected by the temperature detecting means 9, only the voltage applied to the first image carrier squeeze roller 13 by the bias voltage Vs ₁ applying means 110 is changed, and when 15 ° C. is detected by the temperature detecting means 9. Then, only the voltage applied to the second image carrier squeeze roller 13 ′ by the bias voltage Vs ₂ applying means 120 is changed. As described above, the fog toner on the photosensitive member can be efficiently removed by changing one of the squeeze roller applied bias voltage values according to the detected temperature.

（実施例６）
実施例６における印加バイアス電圧値等のパラーメーターを表３に示す。φ７８の像担持体１０で、第１乃至第４のスクイーズローラを設けて、それぞれにバイアス電圧Ｖｓ₁
、バイアス電圧Ｖｓ₂、バイアス電圧Ｖｓ₃、バイアス電圧Ｖｓ₄を印加するようにした。
このような４つのスクイーズローラによれば、より高率でのスクイーズを実現すると共に、感光体上のカブリトナーを効率的に除去することができた。

(Example 6)
Table 3 shows parameters such as an applied bias voltage value in Example 6. The φ78 image carrier 10 is provided with first to fourth squeeze rollers, each of which has a bias voltage Vs _1.
The bias voltage Vs ₂ , the bias voltage Vs ₃ , and the bias voltage Vs ₄ are applied.
According to such four squeeze rollers, squeeze at a higher rate can be realized and fog toner on the photosensitive member can be efficiently removed.

（実施例７）
実施例７における印加バイアス電圧値等のパラーメーターを表４に示す。本実施例においては、像担持体１０として負帯電の感光材料である有機感光体を用い、表４に示すようなバイアス電圧値等の設定を行った上で、各スクイーズローラでカブリトナーを回収したところ、効率的にこれを行うことが可能であった。

(Example 7)
Table 4 shows parameters such as an applied bias voltage value in Example 7. In this embodiment, an organic photoreceptor, which is a negatively charged photosensitive material, is used as the image carrier 10, and after setting the bias voltage values and the like as shown in Table 4, fog toner is collected by each squeeze roller. It was possible to do this efficiently.

なお、本明細書においては、種々の実施の形態について説明したが、それぞれの実施の形態の構成を適宜組み合わせて構成された実施形態も本発明の範疇となるものである。

Note that although various embodiments have been described in this specification, embodiments configured by appropriately combining the configurations of the respective embodiments are also included in the scope of the present invention.

1 is a diagram illustrating main components constituting an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating main components of an image forming unit and a developing device. It is a figure which shows the dark attenuation | damping characteristic of the image carrier used for the image forming apparatus which concerns on embodiment of this invention. FIG. 2 is a diagram illustrating a main configuration of an image forming unit in the image forming apparatus. It is a figure which shows transition of the image carrier surface potential in an image formation process. It is a figure which shows the change of the dark attenuation characteristic by the temperature change of an image carrier. FIG. 2 is a diagram illustrating a main configuration of an image forming apparatus including only one image carrier squeeze roller. It is a figure which shows transition of the image carrier surface potential by the temperature change in an image formation process. FIG. 2 is a diagram illustrating a main configuration of an image forming apparatus including three image carrier squeeze rollers. FIG. 5 is a diagram illustrating main components constituting an image forming apparatus according to another embodiment of the present invention. It is a figure which shows the dark attenuation | damping characteristic of an amorphous silicon photoreceptor and an organic photoreceptor. It is a figure which shows transition of the image carrier surface potential in the image formation process when a negatively charged image carrier is used.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 5 ... Paper feed cassette, 6 ... Pick-up roller, 7, 7 ', 7''... Conveyance roller pair, 9 ... Temperature detection means, 10Y, 10M, 10C, 10K, image carrier, 11Y, 11M, 11C, 11K, corona charger, 12Y, 12M, 12C, 12K, exposure unit, 13Y, first image carrier squeeze roller, 13Y '... second image carrier squeeze roller, 14Y, 14Y' ... image carrier squeeze roller cleaning blade, 16Y ... image carrier cleaning roller, 17Y ... image carrier cleaning roller cleaning blade, 18Y ... Image carrier cleaning blade, 20Y, 20M, 20C, 20K ... Developing roller, 21Y ... Developing roller cleaning blade, 22Y Compaction corona generator, 30Y, 30M,
30C, 30K: Development device, 31Y, 31M, 31C, 31K ... Developer container, 32Y, 32M, 32C, 32K ... Anilox roller, 31Y, 31M, 31C, 31K ... Developer container, 33Y: restriction blade, 34Y: auger (supply roller), 40 ... intermediate transfer member, 41 ... belt drive roller, 42 ... tension roller, 45 ... developer recovery unit, 46 ... Intermediate transfer member cleaning roller, 47 ... Intermediate transfer member cleaning roller cleaning blade, 49 ... Intermediate transfer member cleaning blade, 50Y, 50M, 50C, 50K ... Primary transfer portion, 51Y, 51M, 51C, 51K ... primary transfer backup roller, 52, 53 ... tension roller, 60 ... secondary transfer unit, 61 ... Secondary transfer roller, 62 ... secondary transfer roller cleaning blade, 70Y, 71Y, 72Y, 73Y, 74, 76Y ... (cleaning) blade holding member, 75Y ... regulating blade holding member, 77, 78 ..Cleaning blade holding member, 80Y... Image carrier collection and storage unit, 81Y... Collection screw, 85... Secondary transfer unit collection and storage unit, 86. Body recovery storage unit, 88 ... recovery screw, 90 ... fixing unit, 91 ... heating roller, 92 ... pressure roller, 110 ... bias voltage Vs ₁ applying means, 120 ... bias Voltage Vs ₂ applying means, 130... Rotational speed changing means, 310Y.
Y: collection storage unit, 321Y ... collection screw, 330Y ... partitioning unit, 360Y ... liquid developer supply member, 365Y ... liquid developer supply port, 370Y ... liquid developer supply Tube, 371Y ... Liquid developer recovery tube

Claims (15)

An image carrier;
A charging unit for charging the image carrier;
An exposure unit that exposes the image carrier to form a latent image;
A developing unit that develops the latent image using a liquid developer including a carrier and toner particles;
A first squeeze roller that is in contact with the image carrier developed by the developing unit and to which a bias voltage Vs ₁ is applied;
A second squeeze roller that is in contact with the image carrier squeezed by the first squeeze roller and to which a bias voltage Vs ₂ is applied;
A transfer member in contact with the image carrier squeezed by the second squeeze roller, to which the image is transferred,
The absolute value of the bias voltage Vs _{1 and} the absolute value of the bias voltage Vs ₂ are | Vs ₁ | >> | Vs ₂ |
An image forming apparatus having the following relationship: An image carrier;
A charging unit for charging the image carrier;
An exposure unit that exposes the image carrier to form a latent image;
A developing unit including a developer carrier that is in contact with the image carrier and develops the latent image with a liquid developer including a carrier and toner particles and to which a development bias voltage Vd is applied;
A first squeeze roller that is in contact with the image carrier developed by the developer carrier and to which a bias voltage Vs ₁ is applied;
A second squeeze roller that is in contact with the image carrier squeezed by the first squeeze roller and to which a bias voltage value Vs ₂ is applied;
A transfer member in contact with the image carrier squeezed by the second squeeze roller, to which the image is transferred,
The absolute value of the developing bias voltage Vd, the absolute value of the bias voltage Vs ₁ , and the absolute value of the bias voltage value Vs ₂ are || Vd | — | Vs ₁ ||> || Vs ₁ | — | Vs ₂ ||
An image forming apparatus having the following relationship: Temperature detecting means for detecting the temperature;
The image forming apparatus according to claim 1, further comprising: a bias voltage adjusting unit that changes the bias voltage value Vs ₁ according to a temperature detected by the temperature detecting unit. The image forming apparatus according to claim 3, wherein the bias value adjusting unit changes the bias voltage value Vs ₂ according to a temperature detected by the temperature detecting unit. The image forming apparatus according to claim 4, wherein a change amount of the bias voltage value Vs ₁ is larger than a change amount of the bias voltage value Vs ₂ . The image forming apparatus according to claim 3, further comprising a rotation speed changing unit that changes a rotation speed of the image carrier. The image forming apparatus according to claim 6, wherein the bias value adjusting unit changes the bias voltage value Vs ₁ and the bias voltage value Vs ₂ according to the rotation speed of the image carrier changed by the rotation speed changing unit. apparatus. The image forming apparatus according to claim 7, wherein a change amount of the bias voltage value Vs ₁ is larger than a change amount of the bias voltage value Vs ₂ . The bias voltage adjusting unit increases the absolute value | Vs ₁ | of the bias voltage value and the absolute value | Vs ₂ | of the bias voltage value as the rotational speed of the image carrier increases. Image forming apparatus. A third squeeze roller that is in contact with the image carrier squeezed by the second squeeze roller and to which a bias voltage value Vs ₃ is applied;
The absolute value of the bias voltage Vs _1, the absolute value of the bias voltage Vs ₂ , and the absolute value of the bias voltage value Vs ₃ are | Vs ₁ |> | Vs ₂ |> | Vs ₃ |
The image forming apparatus according to claim 1, wherein: The image carrier is charged by the charging unit,
A latent image is formed by exposing the image carrier in an exposure unit,
The latent image is developed with a liquid developer including a carrier and toner particles in a developing unit including a developing roller that comes into contact with the image carrier,
The image carrier developed by the developing roller is squeezed by a first squeeze roller to which a bias voltage value Vs ₁ is applied,
The image carrier squeezed by the first squeeze roller is squeezed by a second squeeze roller to which a bias voltage value Vs ₂ satisfying | Vs ₁ |> | Vs ₂ | is applied. Forming method. The temperature is detected by the temperature detection means,
The image forming method according to claim 11, wherein the bias voltage value Vs ₁ and the bias voltage value Vs ₂ are changed according to the temperature detected by the temperature detection unit. The image forming method according to claim 12, wherein a change amount of the bias voltage value Vs ₁ is larger than a change amount of the bias voltage value Vs ₂ . Changing the rotation speed of the image carrier by rotation speed changing means;
The image forming method according to claim 11, wherein the bias voltage value Vs ₁ and the bias voltage value Vs ₂ are changed according to the rotation speed of the image carrier changed by the rotation speed changing unit. The image forming method according to claim 14, wherein a change amount of the bias voltage value Vs ₁ is larger than a change amount of the bias voltage value Vs ₂ .

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